To estimate a bound on the lowest nontrivial eigenvalue \(\lambda _{1}\)  one
uses the bound on the Rayleigh quotient [1]}
\(\lambda _{1}=\inf _{\psi \left( U\right) \ne 0}\frac{\int \left( \left|\pi \psi \left( U\right) \right|^{2}+V\left|\psi \left( U\right)\right|^{2}\right) d\mu \left( U\right) }{\int \left|\psi \left(U\right) \right|^{2}d\mu \left( U\right) } \) 
